1. Field of the Invention
The invention relates to reflector lamps having a light-source capsule in a vitreous reflector, and more particularly, to improved lamp structure for securing and aligning the light-source capsule with the reflector. The invention also relates to an improved method of assembly of reflector lamps employing a light-source capsule.
2. Description of the Prior Art
Molded or pressed glass reflector lamps, such as PAR lamps, generally have a reflector portion with a reflective surface and an integrally molded neck portion extending from the rear of the reflector portion. In lamps having a light-source capsule, the capsule is partially disposed within a neck bore, or cavity, which extends from an aperture in the throat of the reflective surface through the neck portion toward the lamp base. Conductive leads extending from the light-source capsule are electrically connected to respective contacts on the lamp base to permit application of an electric potential to the capsule to energize the capsule to emit light.
As used herein, the term "light-source capsule" includes a conventional tungsten filament incandescent capsule, tungsten-halogen capsule, a metal halide arc tube or capsule, a high pressure sodium ceramic arc tube, and any other light-emitting capsule or arc tube mountable within a reflector body.
The assembly of lamps having molded or pressed glass reflectors has historically been achieved by bringing the light-source in from the front of the reflector before further assembly operations, such as lens or base attachment, is performed. The light-source capsule has typically been secured and aligned in the reflector by cementing the capsule in the neck of the reflector, or by soldering, welding, or crimping heavy, rigid lead wires which extend from the capsule to metal parts near the base of the reflector. For glass reflectors including PAR 36, PAR 38, PAR 46, PAR 56, and PAR 64 types, the metal parts are ferrules pressed into and around holes provided in the neck near the lamp base. The light-source capsule is attached to the ferrules by brazing of the capsule lead wires as the first step in lamp assembly. For smaller PAR 20 and PAR 30 reflectors, there is not enough room to attach ferrules using existing glass forming techniques, so eyelets are attached through similar preformed holes. The light-source capsule is attached by crimping or soldering the lead wires to the eyelets. In the above lamps, the light-source capsule must then be focussed by burning the lamp, moving the capsule and bending the lead-wires to align the light-source with the reflector's optical axis. The focussing operation is difficult to automate, so it is typically a manual operation, which is time consuming and increases the cost of the lamp.
For even smaller reflectors such as MR16, MR11 and 35 mm types, even less space is available for preformed eyelet holes. One large hole or slot is formed in the reflector neck and the light-source is dropped in from the front of the reflector, focused, and its press seal cemented in place. Typically, a significant amount of adhesive is required to fill the space surrounding the press seal, which requires lengthy curing times of several hours that increase lamp cost.
Light-source capsules have also been secured within the neck portion of glass reflectors by positioning members secured to the pinch seal of the capsule. In U.S. Pat. No. 4,829,210 (Benson et al.) a disk-shaped positioning member is wedged in the tapered neck bore. However, this has the disadvantage that the small taper angle in the neck causes an appreciable variation in the axial positioning of the light capsule if extremely tight tolerances on the dimensions of the disk and taper angle are not met.
U.S. Pat. No. 4,755,711 (Fields et al.) shows a ceramic reflector lamp in which the halogen light-source is insertable from the rear of the ceramic reflector. The capsule is axially secured in the lamp by fixing the capsule lead-wires in a reservoir of cement in the base, requiring long curing times. The capsule is referenced to the focus of the reflector by reason of a metallic positioning cap, on the end of an elongate non-conventional press seal, which engages the end of internal flutes in the neck bore near the base. The flutes reduce the heat transfer from the capsule to the ceramic reflector.
Aluminized pressed glass reflectors are advantageous because they provide a superior and cost effective reflective surface as compared to reflectors of other materials. However, most glass reflectors require minimum draft angles, to allow for the release of the tooling from the hot glass after the reflector is pressed, which result in limitations in reflector geometry and consequently in lamp performance and assembly. Typically, draft angles of three degrees or more are required both inside and outside the reflector. Since these draft angles open to the front of the reflector, the minimum bore diameter for receiving the end of the light-source capsule, for example a press seal, is spaced from the reflective surface and the bore widens toward the reflective surface. The resulting aperture in the reflective surface is larger than the minimum bore diameter, resulting in a loss of effective reflector surface and reduced lamp efficacy. This is a particularly serious problem with smaller reflector lamps such as MR16's where the reflector surface is already small. The problem is even more serious if the length of the reflector neck must be long to meet maximum base temperature specifications, such as for lamps intended for deep fixtures.
It would be desirable to have a reference surface for the capsule light-source which is accessible from the rear of a pressed glass reflector. However, this is not practical using current glass pressing technology because of the draft angles which open to the front of the reflector. In addition, if a large outside neck diameter is required, as in the case of a lamp using a medium screw type base, the mass of glass which results if a small neck bore size is attempted cannot be reliably controlled using present glass pressing technology.
After the light-source capsule is secured in the reflector neck, a lens or glass cover is usually attached to the rim of the reflector, most commonly with an adhesive. However, water or chemical vapors from the adhesive can be introduced into the lamp between the reflector and lens during the adhesive curing process. If these vapors are not removed from the lamp, they can attack the reflector coating or cause increased gas pressure inside the reflector-lens assembly, which can force the lens to separate from the reflector. Since the light-source is secured in place before the lens is attached, some means of removing the adhesive vapors must be supplied. Usually an exhaust port at the rear of the reflector is used to flush out the vapors after curing, which port must then be sealed off using heat or adhesives. This additional operation also increases lamp cost.
Accordingly, it is an object of the invention to provide a reflector lamp which utilizes the advantages of a glass reflector but which facilitates automated lamp assembly.
A particular object is reduce the size of the aperture in the throat of the reflective surface, for a given neck length and capsule geometry, to increase the area of the reflective surface and improve lamp efficacy.
Still another object is to provide a lamp design that permits necks of increased length to reduce base temperatures without a corresponding decrease in the reflector surface area.
Still a further object is to provide a reflector lamp assembly which accurately locates the light-source capsule within the reflector to obviate the need for separately focusing the light-source with the reflector during lamp assembly.
Another object is to provide an assembly that minimizes the amount of adhesive inside the lamp and in which the curing of the adhesives does not reduce lamp performance.